Intrusion alarm systems typically perform two main tasks: detecting intrusions and responding to intrusions. The task of detecting intrusions is usually performed by way of monitoring one or more sensors that measure one or more of the following: inertia, differential changes in equilibrium, changes in concentrations of harmful substances within some location, vibrations, electrical circuit activations (e.g., opening or closing of a switch), images (e.g., images processed from closed circuit TV), breaks in an optical path, illegal activity on a computer, or other mechanisms.
When responding to intrusions, intrusion alarm systems typically behave in one of three ways. Single-unit alarm systems typically activate individually (“go off”), such as sounding a siren, when disturbed. The main disadvantage of this type of alarm system is that a single alarm siren may not be loud enough to attract the attention of passersby and neighbors. In a second type of alarm system, alarm units alert a central security firm (e.g., Brink's® Home Systems). While surveillance systems that relay signals to a central office are widely deployed and effective in crime reduction, they suffer from the drawback of a lag time between notification and arrival of security agents at the crime scene. In addition, in the event of false alarms, the cost of sending security agents to check for crime is passed on to the end-user as higher service premiums. In a third type of alarm system, an automobile alarm provides a signal to enable security personnel to track and locate the automobile (e.g., LoJack®). Alarm systems equipped with devices for tracking stolen items may not be ideal for a number of reasons: First, they are only activated after theft has been reported to law enforcement authorities and tracking devices have been activated. Hence, they may not prevent or deter theft in the first place. Second, units can only be installed by professionally trained technicians. The infrastructure is complex—often requiring installation of specialized hardware on police cruisers, helicopters, buildings and towers. Such systems are expensive for both the individual and civic governments. Third, such systems only work if the stolen asset is close to a detection unit; the implication of LoJack's availability in 26 states means that the probability of recovering stolen items would be zero in states where the technology is not available. Even in areas where the LoJack technology is available, installation and retrofitting costs can limit its widespread adoption, especially in economically-distressed areas where crime may be highest.